There have been earlier approaches to the draining of partially or fully sealed surfaces with the aid of a seepage system. The method employed to date involves the installation of run-off channels in the sealed sections which channels lead into a system of drain pipes. The major drawback of such a system lies in the fact that, over time, the drain pipes clog up, that servicing these pipes is an extremely complex matter and that the soil around these pipes tends to settle.
The German patent DE 44 03 454 C1 describes a profiled, U-shaped concrete block or drain tile that is open toward the top and serves as the intake section. This intake section is provided with a biological screen the function of which is to biologically filter the incoming water. The lower, horizontal section of the U-block features perforations allowing the water that enters the channel to seep through these perforations into the soil underneath the drain tile. The shortcoming of this channel consists in very limited draining efficiency and the potential for a relatively rapid settling of the soil underneath the concrete block. Moreover, it is quite difficult with this design to compensate for differences in the amount of water collected over the length of the channel, causing fairly quick flooding of the channel in overload situations.
DE 28 35 124 C2 describes a pipe system for soil irrigation and draining. This system consists of two pipes, one inside the other and both partially water-permeable at least in their bottom sections. During the installation, the outer pipe with the larger diameter is slightly flattened so as to give it an ellipsoid profile with a somewhat broader irrigation or drainage capacity. However, a pipe of this type is only suitable for watering and dewatering plants, given that the influx of larger amounts of water, as in the case of drainage systems, could easily cause the soil to pack down.
DE-U-94 15 774 describes a ground cover that can be assembled from profiled, square stone tiles. Water can seep into the grooves between the stone tiles and drain off into the ground through lateral duct channels molded into the tiles. Here again, the problem is relatively quick clogging of the grooves at the points of entry of the drainage water due to the silting effect. Besides, stone tiles of this type cannot be assembled into a contiguous surface in a way as to permit easy movement for instance of shopping carts or forklifts.